Olefin Polymerization catalyst

ABSTRACT

Olefin polymerization catalysts are prepared by depositing an organophosphoryl chromium product and an aluminum compound on an inorganic support material, and heating the support material in a non-reducing atmosphere at a temperature above about 300° C. up to the decomposition temperature of the support material.

This is a division of application Ser. No. 724,484, filed Sept. 20,1976, which is a continuation-in-part of copending application Ser. No.558,504, filed Mar. 14, 1975 now U.S. Pat. No. 3,984,351.

BACKGROUND OF THE INVENTION

The use of chromium compounds in the polymerization of olefins iswell-known. U.S. Pat. Nos. 2,825,721 and 2,951,816 teach the use of CrO₃supported on an inorganic material such as silica, alumina orcombinations of silica and alumina and activated by heating at elevatedtemperatures to polymerize olefins. When these catalyst systems are usedin various polymerization processes such as the well-known particle-formprocess, the resins produced, while useful in many applications, areunsatisfactory for others because of a deficiency in certain propertiessuch as melt index.

Attempts to improve deficient properties of polyolefins produced usingsupported, heat-activated chromium oxide catalysts have been made byadding various metal and non-metal compounds to the supported chromiumoxide prior to activation by heating. For example, in U.S. Pat. No.3,622,522 it is suggested that an alkoxide of gallium or tin be added tosupported chromium oxide prior to heat activation. U.S. Pat. No.3,715,321 suggests adding a compound of a Group II-A or Group III-Bmetal to supported chromium oxide prior to heat treatment whereas U.S.Pat. No. 3,780,011 discloses adding alkyl esters of titanium, vanadiumor boron and U.S. Pat. No. 3,484,428 discloses adding alkyl boroncompounds.

In columns 5 and 6 and Table 1 of U.S. Pat. No. 3,622,522 the additionof aluminum isopropoxide to supported chromium oxide prior to heatactivation is shown for purposes of comparison with the addition of analkoxide of gallium or tin. The patentee concluded that the addition ofthe aluminum compound gave substantially the same or an increasedHLMI/MI ratio of polymers produced as compares to the chromium oxidecatalyst with no metal alkoxide added, whereas the addition of galliumor tin alkoxides produced polymers having a lower HLMI/MI ratio.

It is also known to utilize other chromium compounds as catalysts forthe polymerization of olefins. Such compounds include various silylchromate and polyalicyclic chromate esters as described, for example, inU.S. Pat. Nos. 3,324,095; 3,324,101; 3,642,749; and 3,704,287. The useof phosphorus-containing chromate esters in olefin polymerizationcatalysts has also been disclosed in the aforesaid U.S. Pat. No.3,704,287; and in U.S. Pat. No. 3,474,080 and copending application Ser.No. 532,131, filed Dec. 16, 1974 now U.S. Pat. No. 3,985,676.

Use of the above chromium compound catalysts in Ziegler-typecoordination catalyst systems has also been proposed. As is well-knownin the art, such catalysts frequently additionally compriseorganometallic reducing agents such as, for example, trialkyl aluminumcompounds. Ziegler-type catalyst systems incorporating supportedchromium compound catalysts and organometallic reducing agents,particularly organoaluminum compounds, are disclosed, for example, inU.S. Pat. Nos. 3,324,101; 3,642,749; 3,704,287; 3,806,500; and in theaforesaid copending application Ser. No. 532,131.

SUMMARY OF THE INVENTION

It has been discovered in accordance herewith that olefin polymers, ofsuitable properties e.g. melt indexes and melt index ratios, may besecured at acceptable productivity levels by utilization of an olefinpolymerization catalyst system prepared by depositing anorganophosphoryl chromium product and an aluminum compound on aninorganic support material and heating the supported chromium containingproduct and aluminum compound at a temperature above 300° C. up to thedecomposition temperature of the support. The heat treated, supportedchromium containing product and aluminum compound may be employeddirectly as an olefin polymerization catalyst. Polymers produced usingthe novel catalyst systems of the present invention have desirable flowproperties and shear response.

DETAILED DESCRIPTION OF THE INVENTION

The novel catalyst systems of the present invention are prepared bydepositing, on an inorganic support material having surface hydroxylgroups, an aluminum compound capable of reacting with the surfacehydroxyl groups of the support material and an organophosphoryl chromiumproduct. The supported chromium containing product and aluminum compoundare then heated in a non-reducing atmosphere at a temperature aboveabout 300° C. up to the decomposition temperature of the supportmaterial.

It is believed that the chromium containing product and the aluminumcompound may react with the surface hydroxyl groups on the inorganicsupport material during the course of preparing the novel catalystsystems of the present invention. However, the precise mechanisminvolved is not known and applicants do not wish to be restricted to themechanism postulated above.

The inorganic support materials useful in the present invention includethose normally employed in supported chromium catalysts used in olefinpolymerizations such as those discussed in U.S. Pat. No. 2,825,721.Typically, these support materials are inorganic oxides of silica,alumina, silica-alumina mixtures, thoria, zirconia and comparable oxideswhich are porous, have a medium surface area, and have surface hydroxylgroups. Preferred support materials are silica xerogels or xerogelscontaining silica as the major constituent. Especially preferred are thesilica xerogels described in U.S. Pat. No. 3,652,214 which silicaxerogels have a surface area in the range of 200 to 500 m² /g, a porevolume greater than about 2.0 cc/g, a major portion of the pore volumebeing provided by pores having diameters in the range of 300 to 600 A.

The chromium containing compounds useful in the present inventioncomprise the organophosphoryl chromium compounds disclosed in U.S. Pat.No. 3,985,676 (incorporated herein by reference) which comprise thereaction product of chromium trioxide with an organophosphorus compoundhaving the formula: ##STR1## wherein R is alkyl, aralkyl, aryl,cycloalkyl or hydrogen, but at least one R is other than hydrogen. Thepreferred organophosphorus compounds are trialkyl phosphates such astriethyl phosphate.

Aluminum compounds useful in the present invention are characterized asany aluminum compound capable of reacting with the surface hydroxylgroups of the inorganic support material. Preferred aluminum compoundsmay be represented by the formula:

    Al(X).sub.a (Y).sub.b (Z).sub.c

wherein X is R, Y is OR, and Z is H or a halogen; a is 0-3, b is 0-3, cis 0-3, and a+b+c equals 3; and R is an alkyl or aryl group having fromone to eight carbon atoms.

Examples of such aluminum compounds include aluminum alkoxides such asaluminum sec-butoxide, aluminum ethoxide, aluminum isopropoxide; alkylaluminum alkoxides such as ethyl aluminum ethoxide, methyl aluminumpropoxide, diethyl aluminum ethoxide, diisobutyl aluminum ethoxide,etc.; alkyl aluminum compounds such as triethyl aluminum; triisobutylaluminum, etc.; alkyl or aryl aluminum halides such as diethyl aluminumchloride; aryl aluminum compounds such as triphenyl aluminum, aryloxyaluminum compounds such as aluminum phenoxide and mixed aryl, alkyl andaryloxy, alkyl aluminum compounds.

The novel catalysts of the present invention may be prepared bydepositing the organophosphoryl chromium product and the aluminumcompound on the inorganic support in any suitable manner such as byvapor coating or by impregnating the support with solutions thereof in asuitable inert solvent which is normally an anhydrous organic solvent.Such organic solvents include aliphatic, cycloalkyl, and alkylarylhydrocarbons and their halogenated derivatives. A preferred organicsolvent is dichloromethane. The chromium containing-product may beapplied to the support first or the aluminum compound may be appliedfirst or the chromium and aluminum compound may be applied together. Inapplicants' usual method of catalyst preparation, the support isimpregnated first with the chromium-containing product and then thealuminum compound.

Preferably the organoaluminum compound may be applied to the catalystsupport under conditions similar to those utilized for deposition of theorganophosphoryl chromium compound.

The most effective catalysts have been found to be those containing thechromium in an amount such that the amount of Cr by weight based on theweight of the support is from about 0.25 to 2.5% and preferably is fromabout 0.5 to 1.25%, although amounts outside of these ranges still yieldoperable catalysts. The aluminum compound should be added in sufficientamounts to provide from about 0.1 to 10% of aluminum by weight based onthe weight of the support and preferably from about 0.5 to 5.5% althoughother amounts outside of these ranges can be used to prepare operablecatalysts.

After the chromium containing product and the aluminum compound havebeen deposited on the inorganic support, the support is heated in anon-reducing atmosphere, preferably in an oxygen containing atmosphere,at a temperature above about 300° C. up to the decomposition temperatureof the support. Typically, the supported compositions are heated at atemperature of from 500° to 1000° C. The heating time may vary, forexample, depending on the temperatures used, from 1/2 hour or less to 50hours or more. Normally the heating is carried out over a period of 2 to12 hours. The non-reducing atmosphere which is preferably air or otheroxygen containing gas should be dry and preferably should bedehumidified down to a few parts per million (ppm) of water to obtainmaximum catalyst activity. Typically, air used in the proceduredescribed in this application is dried to less than 2-3 ppm of water.

The heat-treated supported chromium and aluminum materials of thepresent invention may be used directly as an olefin polymerizationcatalyst i.e., in the absence of a reducing agent as shown in theExamples. Such catalysts may also of course be employed in combinationwith metallic and/or non-metallic reducing agents as disclosed andclaimed in U.S. Pat. No. 3,984,351.

The catalyst compositions of this invention are amenable to use withconventional polymerization processes for olefins, in particular1-olefins having 2-8 carbon atoms and are suitable for polymerizationeffected under temperature and pressure conditions generally employed inthe art, e.g., temperatures of from about 40° C. to about 200° C. andpreferably from about 70° C. to 110° C. and pressures of from 200 to1000 psig and preferably from 300 to 800 psig, as are used in slurry orparticle form polymerizations.

EXAMPLE 1 I. CATALYST PREPARATION PROCEDURE

A. Polypor silica xerogel having a pore volume of about 2.5 cc/gprepared in accordance with the disclosure in U.S. Pat. No. 3,652,215 isadded to a 2000 ml, three-neck round bottom flask equipped with astirrer, nitrogen inlet and y-tube with water condenser. A nitrogenatmosphere is maintained during the coating operation. Dichloromethaneis then added to the flask containing the silica gel and stirring iscommenced to insure uniform wetting of the gel. A dichloromethanesolution of the reaction product of CrO₃ and triethyl phosphate preparedas described in U.S. Pat. No. 3,985,676 is then added to the flask insufficient quantity to provide a dry coated catalyst containing about 1%by weight of Cr. The supernatant liquid is removed by filtration and thecoated gel is dried in a rotary evaporator at 60° C. and with 29 inchesof Hg vacuum.

B. Dichloromethane is added to a similar flask as used in step A andwhile maintaining a nitrogen atmosphere stirring is commenced. To theflask is added the supported chromium composition prepared in step Aabove. A solution of dichloromethane and aluminum sec-butoxide isprepared in a pressure equalizing dropping funnel and the funnelattached to the stirred flask. The aluminum sec-butoxide solution isgradually added to the flask at the rate of 10 grams of solution perminute. After the addition of the solution is complete the slurry in theflask is stirred for about 1 hour. The supernatant liquid is removed byfiltration and the coated gel is dried in a rotary evaporator attemperatures up to about 60° C. and 29 inches Hg vacuum. The amount ofaluminum compound added depends on the % aluminum desired for theproduction of olefin polymers having specific properties necessary forcertain end use applications.

C. To heat activate the catalyst composition prepared in step B, thesupported catalyst is placed in a cylindrical container and fluidizedwith dry air at 0.20 feet per minute lineal velocity while being heatedto a temperature of 900° C. and held at this temperature for six hours.The activated supported catalyst is recovered as a powder.

II. POLYMERIZATION

The polymerizations were carried out in a stirred autoclave usingisobutane as a diluent. The supported organophosphoryl chromium reactionproduct and aluminum compound is added along with the isobutane solventto a stirred one gallon autocalve. The contents of the stirred autoclaveare then heated to the polymerization temperature, i.e., 88° to 108° C.Hydrogen, if used, is added and then the ethylene is added to give 10mol% in the liquid phase at which time the total pressure will be fromabout 425 to 455 psig. Polymerization begins almost immediately as notedby the ethylene coming from the ethylene demand supply to the reactor.After approximately one hour of polymerization, the reaction isterminated by dropping the reactor contents into a pressure let-downsystem. The melt index (M.I.) and the high load melt index (HLMI) of thepolymers prepared were determined using ASTM D-1238-65T (conditions Eand F respectively)

III. A series of polymerizations were carried out comparing catalystswith and without the aluminum compound present. The catalysts wereprepared as in the Catalyst Preparation Procedure above, except that thealuminum compound of step B was omitted where indicated. Thepolymerizations were carried out at about 99° C. and hydrogen was addedto the reactor as indicated. No reducing agent catalyst component wasemployed.

                  TABLE I                                                         ______________________________________                                        Al %            Productivity                                                  Wt./SiO.sub.2                                                                        H.sub.2 (psi)                                                                          (gm PE/gm cat./hr.)                                                                            MI    HLMI                                   ______________________________________                                        None   0         622             0.26  27.8                                   3.7    0        1032             0.71  53.6                                   None   30        190             0.58  43.9                                   3.7    30       1399             0.75  58.2                                   ______________________________________                                    

EXAMPLE 2

Catalysts prepared with and without the aluminum compound were comparedin the following olefin polymerizations. The catalysts were preparedidentically (except for the omission of the aluminum compound, asindicated) utilizing a spray coating technique substantially in accordwith the Catalyst Preparation Procedure above except that minimumsolvent is employed, about equivalent to one pore volume of solvent forthe silica gel (2.2-2.4 cc/g.).

In these polymerizations (carried out in accordance with the procedureoutlined in Example 1) no hydrogen was employed, and no reducing agent.The results were obtained as follows:

                  TABLE II                                                        ______________________________________                                        Al %   Productivity                                                           Wt./SiO.sub.2                                                                        (gm Pe/gm cat./hr.)                                                                            MI     HLMI  HLMI/MI                                  ______________________________________                                        3.7    552              2.96   162   54.7                                     None   390              1.11    66   59.5                                     ______________________________________                                    

What is claimed is:
 1. A process for the polymerization of 1-olefinscomprising providing at least one 1-olefin to an enclosed polymerizationzone maintained at elevated temperature and pressure and comprising anolefin polymerization catalyst system consisting essentially of:(a) asolid inorganic support material having surface hydroxyl groups, (b) anorganophosphoryl chromium reaction product of chromium trioxide and aphosphorus compound having the formula: ##STR2## wherein R is alkyl,aralkyl, aryl, cycloalkyl or hydrogen, but at least one R is other thanhydrogen, said reaction product being deposited on said support (c) analuminum compound deposited on said support, said aluminum compoundbeing capable of reacting with said surface hydroxyl groups, saidsupported chromium containing compound and aluminum compound having beenheated in a non-reducing atmosphere at a temperature above 300° C. up tothe decomposition temperature of the support material.
 2. The process ofclaim 1 wherein the aluminum compound is represented by the formula:

    Al(X).sub.a (Y).sub.b (Z).sub.c

wherein X is R, Y is OR and Z is H or halogen; a is 0-3, b is 0-3, c is0-3, and a+b+c=3; and R is an alkyl or aryl group having from one toeight carbon atoms.
 3. The process of claim 1 wherein the inorganicsupport material is a silica gel having a surface area of 200 to 500 m²/g, a pore volume above 2.0 cc/g, a major portion of the pore volumebeing provided by pores having diameters of 300 to 600 A.
 4. The processof claim 1 wherein the chromium containing compound is present in anamount sufficient to provide about 0.25 to about 2.5% by weight of Crbased upon the weight of the support and the aluminum compound ispresent in an amount sufficient to provide about 0.10 to about 10% byweight of Al based upon the weight of the support.
 5. The process ofclaim 1 wherein the chromium containing compound is the reaction productof chromium trioxide and triethyl phosphate.
 6. The process of claim 1wherein the chromium containing compound is the reaction product ofchromium trioxide and triethyl phosphate and the aluminum compound isaluminum sec-butoxide.
 7. The process of claim 1 wherein thepolymerization temperature ranges from about 40° to about 200° C. andthe polymerization pressure ranges from about 200 to about 1000 psig.